1. Technical Field
The present invention relates to a gas-insulated switchgear, and particularly to a resin mold bushing thereof.
2. Background Art
FIGS. 5 and 6 show an example of one of conventional gas-insulated switchgears in which a resin mold bushing of a type shown therein is used.
Referring to the sectional view of FIG. 5 showing the gas-insulated switchgear, reference numeral 1 is a tank of ground potential (hereinafter referred to as a ground tank) hermetically sealed from the air, and insulating gas (SF6 gas in this case) is enclosed in the ground tank. Numeral 2 is a breaker, numeral 103 is a resin mold bushing for supporting and insulating an internal conductor 7 from the ground tank 1, numeral 4 is a disconnector blade, and numeral 5 is a blade-supporting conductor for rotatably supporting the disconnector blade 4. Numeral 6 is a disconnector-fixing terminal that is engaged with the disconnector blade 4 due to turning of the disconnector blade 4 and energizes electrically, and the disconnector-fixing terminal is fixedly supported in the ground tank 1 by an insulating material not shown in the drawing. The blade-supporting conductor 5 is fixed at and electrically connected with one end in the ground tank 1 of the internal conductor 7, and the other end of the internal conductor 7 is connected with electrical machinery and apparatus or the like not shown in the drawing. Though the breaker, disconnector, bushing, and so on for three phases are actually accommodated in the ground tank, and one phase thereof is mainly shown in the drawing.
FIG. 6 is a sectional view showing the construction of the disconnector portion in FIG. 5 in detail. The internal conductor 7 and a shield 108 surrounding the internal conductor 7 are embedded in the resin mold bushing 103, and the resin mold bushing 103 is fixedly supported on the ground tank 1 by an outermost circumferential flange portion of the resin mold bushing 103 with a nut 10 and a male screw 9 that is fixed on the ground tank 1 and extends through a fixing seat 108a of this flange portion. The shield 108 possesses the metal fixing seat 108a through which the male screw 9 extends in the outer circumferential portion thereof, a cylindrical shield portion 108b composed of a metal net and arranged to be concentric with the internal conductor 7 in the central portion thereof, and a metal bar 108c joining the fixing seat 108a and the cylindrical shield portion 108b. 
The resin mold bushing 103 is normally composed of epoxy resin, and when the resin mold bushing 103 is manufactured, exfoliation (peeling) force is generated at the boundary between the shield and the epoxy resin and exfoliation often occurs due to difference between a coefficient of thermal expansion of the epoxy resin and that of the metal composing the shield 108 in the process of curing and shrinking of the epoxy resin. Therefore, in the process of curing and shrinking of the epoxy resin, it is necessary that the shield have elasticity following this curing and shrinking. For this reason, the metal net is used for the cylindrical shield portion 108b. The cylindrical shield portion 108b is formed netlike, and therefore the shield 108 is manufactured by joining the parts with each other through soldering or the like.
In the gas-insulated switchgear employing the resin mold bushing of the foregoing construction, a main circuit current flows a passage through the internal conductor 7, the blade-supporting conductor 5, the disconnector blade 4, the disconnector fixed terminal 6, and the breaker 2 in the order. The cylindrical shield portion 108b prevents electric-field concentration at an edge portion 1a of the ground tank 1.
In the conventional gas-insulated switchgear of the foregoing construction, the resin mold bushing is solid, and an upper end thereof is provided with the blade-supporting conductor 5. As a result, it is not possible to diminish the height, and this makes it difficult to miniaturize a gas-insulated switchgear.
Moreover, the shield 108 of the resin mold bushing is constructed by joining the metal constituent members with each other through soldering or the like, and this causes a problem that manufacturing the shield requires much time and labor.
The present invention was made to solve the above-discussed problems and has an object of obtaining a gas-insulated switchgear having a construction in which it is possible to diminish height of a disconnector and miniaturize the gas-insulated switchgear.
Another object of the invention is to obtain a gas-insulated switchgear in which a shield of a resin mold bushing has a simple configuration so that the shield may be integrally formed into one body and the resin mold bushing is manufactured easily.
A gas-insulated switchgear according to the invention comprises: a ground potential tank in which insulating gas is hermetically enclosed; a breaker and a disconnector accommodated in the mentioned tank; a resin mold bushing for supporting and insulating a main circuit conductor connected with the mentioned disconnector from the tank, the resin mold bushing possessing a container portion with an end opened at inside of the tank and being fixedly supported on the tank; and a blade-supporting conductor being connected with the main circuit conductor insulated and supported by the mentioned resin mold bushing, the blade-supporting conductor being installed in the mentioned container portion and supporting a disconnector blade of the mentioned disconnector.
As a result, this blade-supporting conductor can be accommodated in the container portion of the resin mold bushing, and it is possible to make the switchgear compact.
It is preferable that the resin mold bushing of the gas-insulated switchgear according to the invention molds an electric-field relaxation shield is comprised of: an electric-field relaxation shield portion composed of a annular metal plate surrounding the main circuit conductor; a cylindrical fixing seat for fixing the tank installed outside the mentioned electric-field relaxation shield portion; and a metal bar for joining the electric-field relaxation shield portion and the fixing seat integrally into one body; and that the resin mold bushing also molds the container portion surrounding the main circuit conductor and having one end opened.
As a result, it is possible to follow internal stress at the time of manufacturing the resin and prevent exfoliation on the boundary between the resin and the metal, and the electric-field relaxation shield is easily manufactured into an integral construction through a manufacturing method such as casting. The blade-supporting conductor can be accommodated in the container portion of the resin mold bushing, and it is possible to make the switchgear compact.
It is also preferable that the annular electric-field relaxation shield portion is provided with a slit.
As a result, it is possible to more sufficiently follow the internal stress at the time of manufacturing the resin and more successfully prevent exfoliation on the boundary between the resin and the metal.